Currently, there are various mechanisms for ejecting ink from an ink reservoir. For example, US Patent Publication 2006/0232631 A1 discloses an ink reservoir having a piston in the ink reservoir which is movable to cause ink to be ejected from the reservoir. The piston is connected to a heating element that is energized that causes the heating element to expand which, in turn, causes the piston to move to eject the ink. Although pistons are satisfactory, improvements are always desirable. For example, heating elements usually require a high input voltage which is not desirable.
While not an ink ejecting system, U.S. Pat. No. 6,811,133 B2 discloses a hydraulic system having a primary movable membrane with a piezoelectric material and a secondary movable membrane. Fluid is disposed between the primary and secondary membrane, and the piezoelectric material of the primary membrane is energized for causing the primary membrane to bow which, in turn, causes the secondary membrane to bow. The bowing of the secondary membrane functions as a valve in which the valve is opened and closed according to movement of the secondary membrane. Consequently, valve structures of this type are not needed for inkjet printing devices to eject ink.
Existing thermal inkjet actuators (bubble jet) boils ink directly to produce vapor bubbles to eject liquid drops. Such devices have limited ink latitude (aqueous based inks only) and suffer from reliability problems related to kogation (solid deposits baked onto the surface of the heater surface) and heater failure due to repeated heating to high temperatures. Existing non-thermal inkjet actuators (piezo-actuator or electrostatic actuator) have much wider ink latitude (aqueous and non-aqueous based inks) as well as longer lifetime. However, such actuators have small (sub-micron) displacement; therefore, a large actuator area is needed to displace sufficient amount of liquid to produce desired drop volume. As a result, it is very difficult to achieve high nozzle density required for high-resolution printing. Also, high voltage or high current are needed to activate such inkjet actuators, which require expensive and complicated drive electronics and limit maximum operating frequency.
Consequently, a need exists for a non-thermal ink ejecting mechanism in which large actuator displacement can be achieved with low input voltage or energy.